Insulation inspection system with voltage and current balancing circuit

The information provided in this section is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

The present disclosure relates to continuity testing systems, and more particularly, to insulation inspection systems for inspecting stator windings and other electrical components.

Electric vehicles and hybrid vehicles include traction motors for propulsion purposes. Each of the traction motors includes a stator and a rotor having corresponding windings and conductive bars. The windings and/or conductive bars may be insulated (e.g., have an outer insulative coating). During manufacturing, including part and component formation and assembly, the insulative coatings may not be formed properly or may be nicked, scratched, rubbed, etc. This can result in portions of the insulative coatings being absent and/or removed thereby exposing electrically conductive elements. This exposure can result in a short circuit, affect motor performance, and/or reduce life of the motor.

An insulation inspection system is disclosed and includes: a set of input terminals; a brush; a circuit connected to the set of input terminals, the brush, and a part being inspected, where the circuit includes at least one pair of resistors and a capacitor; and a control module configured to detect when a short circuit exists between a conductive element of the part and one or more conductive bristles due to insulative material missing on the part and as a result the one or more conductive bristles of the brush contacting the conductive element of the part.

In other features, the set of input terminals includes a positive terminal and a negative terminal. The capacitor and a first resistor of the pair of resistors is connected in series between the positive terminal and the negative terminal.

In other features, the set of terminals includes a common terminal separate from the positive terminal and the negative terminal. A second resistor of the pair of resistors is connected between the negative terminal and the common terminal.

In other features, the set of terminals includes a positive terminal, a negative terminal and a common terminal. The circuit is implemented as a voltage and current balancing circuit and includes the pair of resistors and the capacitor connected in series between the positive terminal and the common terminal. A first resistor of the pair of resistors and the capacitor are connected in series between the positive terminal and the negative terminal. A second resistor of the pair of resistors is connected between the negative terminal and the common terminal.

In other features, the capacitor is connected across a power source and between the positive terminal and the negative terminal.

In other features, the first resistor includes i) a first end connected to a first end of the capacitor, and ii) a second end connected to a first one of the set of input terminals and to the brush. The second resistor includes i) a first end connected to a second one of the set of input terminals, to a second end of the capacitor, and to the part, and ii) a second end connected to a third one of the set of input terminals.

In other features, the first end of the capacitor is connected to a positive terminal of the power source. The second end of the capacitor is connected to a negative terminal of the power source.

In other features, a lead is connected between i) the second one of the set on input terminals, the first end of the second resistor and the second end of the capacitor, and ii) one or more 3-phase contacts of the part.

In other features, the insulation inspection system further includes an analog-to-digital converter connected to the circuit and configured to convert an analog signal output from the circuit to a digital signal. The control module is configured, based on the digital signal, to detect when a short circuit exists between the conductive element of the part and the one or more conductive bristles.

In other features, the control module is configured to generate at least one of a message or an alarm when a short circuit between the conductive element of the part and the one or more conductive bristles is detected.

In other features, an insulation inspection method is disclosed and includes: connecting a lead to a part to be inspected; moving a brush across a portion of the part or moving the part relative to the brush; detecting via a circuit a drop in voltage across a pair of input terminals, where the circuit is connected to the pair of input terminals, the brush, and the part, and where the circuit includes at least one of a pair of resistors and a capacitor; and determining whether the drop in voltage is indicative of when a short circuit exists between a conductive element of the part and one or more conductive bristles of the brush due to insulative material missing on the part and as a result the one or more conductive bristles of the brush contacting the conductive element of the part.

In other features, the set of input terminals includes a positive terminal and a negative terminal. The capacitor and a first resistor of the pair of resistors is connected in series between the positive terminal and the negative terminal.

In other features, the set of terminals includes a common terminal separate from the positive terminal and the negative terminal. A second resistor of the pair of resistor is connected between the negative terminal and the common terminal.

In other features, the set of terminals includes a positive terminal, a negative terminal and a common terminal. The circuit is implemented as a voltage and current balancing circuit and includes the pair of resistors and the capacitor connected in series between the positive terminal and the common terminal. A first resistor of the pair of resistors and the capacitor are connected in series between the positive terminal and the negative terminal. A second resistor of the pair of resistors is connected between the negative terminal and the common terminal.

In other features, the capacitor is connected across a power source and between the positive terminal and the negative terminal.

In other features, the pair of resistors includes a first resistor and a second resistor. The first resistor includes i) a first end connected to a first end of the capacitor, and ii) a second end connected to a first one of the set of input terminals and to the brush. The second resistor includes i) a first end connected to a second one of the set of input terminals, to a second end of the capacitor, and to the part, and ii) a second end connected to a third one of the set of input terminals.

In other features, the first end of the capacitor is connected to a positive terminal of a power source. The second end of the capacitor is connected to a negative terminal of the power source.

In other features, a lead is connected between i) the second one of the set of input terminals, the first end of the second resistor and the second end of the capacitor, and ii) one or more 3-phase contacts of the part.

In other features, the insulation inspection method further includes: converting an analog signal output from the circuit to a digital signal via an analog-to-digital converter, where the analog-to-digital converter is connected to the circuit; and based on the digital signal, detecting when a short circuit exists between the conductive element of the part and the one or more conductive bristles.

In other features, the insulation inspection method further includes generating at least one of a message or an alarm when a short circuit between the conductive element of the part and the one or more conductive bristles is detected.

Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

In the drawings, reference numbers may be reused to identify similar and/or identical elements.

During manufacturing, motors may be inspected to detect defects such as defects in insulative coatings of electrical elements of a stator. The insulative coatings may be visually inspected. This may include a quality control technician using a magnifying glass to visually inspect for defects in the insulative coatings of the stator. Such an inspection is labor intensive and is subject to limitations of the technician. A continuity tester may be used that applies a voltage to the stator and detects when a short circuit exists. Electrical current flows between the stator and the continuity tester when there is a lack of insulative material at the where the tester contacts the stator.

The continuity tester may include a brush that includes conductive bristles. The bristles may be moved across and brush various portions of the stator to detect short circuit locations (i.e., defect locations) where there is a lack of insulative material. The opposite may also occur where the part (or stator) is moved through the bristles and the brush is stationary. A circuit is used to monitor changes in a voltage at the brush. The voltage drops off substantially when a short circuit occurs. There are large swings in voltage and current between when no short exists and when a short does exist.

Large voltage and current swings in the circuit can be detrimental to components over time if not managed properly. Thus, the components can degrade over time and as a result this degradation can negatively affect operation of the circuit. For example, an A/D converter may have specific voltage and current restrictions for operation based on what is used. If there is any resulting drift in circuit components such as in resistors or other circuit components, this can result in voltage response behaviors that can cause issues with voltage threshold setting and not appropriately detecting a short. The degradation of the circuit components can cause drift in the voltage, which can result in subsequent defects going undetected. The drift thus requires circuit adjustments and periodic recalibrating including adjustments in a threshold value. A defect may be detected when the voltage drops below the threshold value. As an example, the threshold value may be set at 5 volts (V), which is significantly lower than a nominal and/or normally expected voltage (e.g., 24V). The threshold value may be set at less than or equal to 20% of the nominal voltage.

The drift can also result in unsafe current levels. If circuit components degrade over time and a resulting change in expected current of the circuit occurs, this can lead to current levels in the circuit that can exceed a threshold for perceived and/or actual bodily harm. In addition, higher than expected current levels can also be detrimental to parts and the brush even when human exposure is mitigated.

The examples set forth herein include an insulation inspection system having a voltage and current balancing circuit, as shown in. The voltage and current balancing circuit provides a balanced voltage response at a nominal low current that is detected via bristles of a continuity testing brush used to detect a defect (or short). The voltage and current balancing provides stability, improves longevity of circuit components, and provides improved functionality allowing for use of the insulation inspection system in various applications while being human touch safe. The insulation inspection system, in addition to the stated hardware, further includes an algorithm for flagging defective parts. The algorithm improves sensitivity for better detection of defects.

The voltage and current balancing circuit improves flexibility in safety by incorporating a capacitor for voltage distribution and resistors Rand Rof appropriate size. The resistors Rand Rare selected to generate a low current response. The capacitor and resistors are connected across common, negative and positive terminals of an analog-to-digital (A/D) converter. The values of the resistors Rand Rare selected to generate a low current response during throughout operation and/or at all points of operation of the voltage and current balancing circuit. The low current response makes the test setup safe for an operator. The capacitor produces an open-circuit condition when an electrical short does not exist. When a short is detected using a brush (e.g., a brush having carbon bristles), a voltage at a positive end of the capacitor drops, which results in some drop in voltage across the resistors Rand Rsuch that voltages of each positive and negative terminal of the A/D converter remains within a predetermined voltage range (e.g., ±13V) relative to a voltage on the A/D common terminal.

The selection of the resistors Rand Ris done such that the current throughout the voltage and current balancing circuit when there is a short is maintained below a predetermined current (e.g., less than or equal to 25 mA, which is not perceptible by human contact). From an incoming analog voltage signal standpoint, this would have the positive terminal of the A/D converter maintained at the nominal operating voltage (e.g., 24 V) and the negative terminal of the A/D converter maintained at 0 V when no short is present. When a break in insulation occurs, i.e., the brush to phase lead connection is shorted, the following changes occur in the voltage and current balancing circuit. The positive A/D terminal is forced towards 0V. It is worth noting that the positive A/D terminal may not fully reach 0V due to intermittent contact between the brush bristles but in the case of a solid short being formed the positive A/D terminal is forced to 0V. A defect is detected when the positive A/D terminal drops to or below a predetermined threshold (e.g., 5V) or lower compared with the base or no short nominal voltage (e.g., 24V).

Since the negative A/D terminal is maintained at 0V, there is a 0V difference between the positive and negative A/D terminals, and by consequence the common A/D terminal is at 0V as well. Because of this, resistor Rconnected across the negative and common A/D terminals experiences a 0V drop (no current flow).

When a defect is detected, the capacitor will have charge available to discharge as needed rather than having a power source, supplying the nominal voltage, be directly connected to the short (or defect). This allows for a constant voltage drop of the capacitor to be maintained while minimizing an amount of current flow in any branch of the voltage and current balancing circuit as the corresponding brush makes intermittent contact with the defect. This is done by maintaining a resistor-capacitor (RC) time constant sufficiently long such that discharge of the capacitor does not cause large swings in a voltage drop across the capacitor over the time duration that intermittent contact is made between the brush and the defected area. As an example, the time constant may be 24 seconds. This results in a resistor Rbeing connected between i) the capacitor and ii) the positive A/D terminal and the brush, primarily experiencing the voltage drop when a short condition occurs.

To make certain that current in the circuit does not exceed something that the human body would be able to perceive, resistor Ris selected such that when a short exists the current will not exceed a threshold (e.g., 1 milli-ampere (mA)). This voltage and current balancing at all points of operation is what allows the entire voltage and current balancing circuit to be safe for human touch as well as not introduce current or voltage levels that would damage either brush bristles or a part being inspected. The current and voltage levels remain below predetermined thresholds to prevent, for example, arcing.

When a short exists, the capacitor may be discharged at an appropriate rate for rapid stable measurement. Current flows through the resistors and provides an analog voltage measurement for the A/D converter. Once the brush is removed from the defect and a short circuit no longer exists, the capacitor is charged until it is back in an open-circuit state.

The voltage and current balancing circuit prevent deterioration of circuit components by preventing large swings in voltage and current across circuit components in the event of a short. The values of the capacitor and resistors are selected for improved circuit performance and to prevent circuit component deterioration due to parasitic voltages across the resistors. The values are selected to prevent drifting of circuit component values. This prevents larger than expected voltage drops and arcing across bristles of the brush.

shows a portionof a stator. The stator includes welded wire pairs that are coated in insulative material. The portionincludes a defectwhere a portion of the insulative coatingis missing and conductive materialof a wire is exposed. Ina bottom (or welded end) of the stator is shown. The stator includes a laminated stack (or body)having a bottom faceand multiple ears (one earis shown in). As an example, the insulative coatingmay be epoxy.

shows an insulation inspection systeminspecting a stator. The insulation inspection systemincludes a human machine interface (HMI)and a voltage and current balancing circuit, which is connected to a power source. The HMImay include a control module, an A/D converter, a memory, a transceiver, a display, and an audible device. The displayincludes LEDsand/or other visual display and/or indicator elements. The control modulereceives digital voltage data from the A/D converter, which receives an analog input signal from the voltage and current balancing circuit. The control moduledetects defects when the analog output signal across positive and negative terminals,(or corresponding digital signal) of the A/D converterdrops in voltage below the threshold (e.g., 5V or 20% of nominal or normal expected voltage (e.g., 24V)). The normal expected voltage with no detected defect may be 24V. The control modulemay indicate detection of defects via the displayand audible device. Detection of a defect, the change (or drop) in voltage, the timing of the detection, and/or other related information may be stored in the memory. As an example, the detection of the defect may be stored along with a proximate location of the defect relative to one or more reference points on the stator.

The displayprovides a visual aid for indicating detection of a defect. This provides an indication also of when a defect is detected. The audible devicemay provide a loud sound such as a loud alarm signal when a defect is detected. The audible devicemay include, for example, a speaker. The control modulemay report detected defects and corresponding information stored in the memoryto one or more network devices remotely located from the HMIvia the transceiver.

The voltage and current balancing circuitincludes resistors R, Rand a capacitor C. Resistor Rhas i) a first end connected to a first (or positive) terminal of the A/D converterand to the brush, and ii) a second end connected to a first end of the capacitor C and to a positive terminal of the power source. Resistor Rincludes i) a first end connected to second (or negative) input terminalof the A/D converter, to a second end of the capacitor, one or more of the 3-phase contacts, and a negative terminal of the power source, and ii) a second end connected to a third (or common) terminal COM of the A/D converter. The common terminal COM is separate from and not connected to either of the terminals,. A leadis connected between i) the negative terminal, the first end of resistor Rand the second end of capacitor C, and ii) the one or more 3-phase contacts. The first end of the capacitor C is connected to the positive terminal of the power source. A second end of the capacitor C is connected to the negative terminal of the power source.

The resistors R, Rand the capacitor C are connected in series between the terminaland the common terminal COM. In the example shown, the capacitor C is connected between the resistors Rand R. In an embodiment, the resistors Rand Rare directly connected to the terminals,and directly connected to the capacitor C. The resistor Rmay be directly connected to the brush. The resistor Rmay be directly connected to the stator.

As an example, the resistor Rmay be 20-30 kiloohms (kΩ), the resistor Rmay be 400-500 kΩ, and the capacitor may be 500-1500 microfarads (μF). In an embodiment, Ris 24 kΩ, Ris 470 kΩ, and C is 1000 μF. The resistances of the resistors and the capacitance of the capacitor are selected to provide the RC time constant referred to herein. In an embodiment, the resistances of the resistors R, Rare selected to limit an amount of current flowing through the stator, the voltage and current balancing circuit, and the brush. The resistances of the resistors Rand Rand the capacitance of the capacitor C are selected i) to prevent arcing and sparking at the bristleswhen a defect (short circuit) occurs, and ii) for proper current balancing in the circuit during all test conditions to maintain being safe for human touch (less than 1 mA). For example, the resistances of the resistors Rand Rmay be selected to prevent the current through the circuit, the brushand the statorfrom exceeding a predetermined threshold.

The resistance values are selected to limit current during all aspects of operation and to balance the voltage load permitted across the channels of the A/D convertersuch as that associated with the terminals,. In an embodiment and regardless of whether a defect is present (short occurs) or no defect (no short) is present, the current is maintained between 25 microamperes (uA) and 1 mA due to i) the placement and selected values of resistors Rand Ralong with the capacitor C in the voltage and current balancing circuitin relation to the power source(e.g., 24 VDC power supply), and ii) A/D voltage channel limits between different channels relative to the A/D common terminal COM. The resistances of Rand Rmay be changed based on A/D behavior limits to maintain the current behavior described. As an example, the channel limits may be such that the A/D channels of the A/D converter are within ±10-13V of the A/D common terminal COM. In an embodiment, the channel limits are such that the A/D channels are within ±10.2V of the A/D common terminal COM.

The capacitance rating of the capacitor C is selected to provide a sufficiently long RC time constant in conjunction with the Rvalue selected for current level reasons. This is done to provide a stable nominal voltage (e.g., stable 24V) to the voltage and current balancing circuitwithin the time window it takes to determine if a short has occurred. The R*C value may provide a time constant of approximately 24 seconds. This provides a sufficiently long time constant that does not need to be increased further with a larger C value, however the time constant may be increased further. If the time constant is too small then the charging and discharging behavior of the capacitor C would influence circuit operation in that the nominal voltage would no longer stay at a stable 24V when a defect occurs. This can make it challenging to assign a specific defect detection threshold since the voltage response would become convoluted with the behavior of the capacitor C.

The capacitance of the capacitor C affects a rate of change in current flowing through the stator, the voltage and current balancing circuit, and the brush. The capacitor C is included as a safeguard for the brushand bristlesand prevents a surge in current from the power sourceto the location of the short circuit. When no short circuit exists, the capacitor C is charged. When a short circuit exists, the capacitor C discharges. The capacitor C does not fully discharge due to the RC time constant used. This aids in limiting current in the circuit during a shorting event. After the discharge, the power sourcerecharges the capacitor C. Typically if the bristles are being moved, the short circuit lasts a short period of time. Without the capacitor C, the resistors Rand Rmay deteriorate due to a short circuit and surge in current through the resistors Rand R. The capacitance and resistance values may also be selected based on the application of use to provide a low current draw for safe operator use. For example, the capacitance of the capacitor C and the resistances of the resistors R, Rmay be selected to accommodate different brush head designs used for detecting defects. In an embodiment, the brush is designed to have a low impedance compared with the circuit components. The insulation inspection systemis able to accommodate brushes having various different designs.

The HMIand/or A/D converterdetects an analog voltage across the terminals,. Filtering of the A/D signal is done through data sampling to remove noise associated with electrical behavior of the bristles of the brush. A voltage from the power sourceis provided across the capacitor C, which provides a stable voltage in conjunction with resistor Rto the brushand one of the 3-phase contactsof the statoris connected to the lead. When one or more of the bristles, which are conductive, comes in contact with an exposed conductive element of the statorcurrent flows from one of the 3-phase contactsthrough the statorand to one or more of the bristlesthat are in contact with the exposed conductive element. The 3-phase contactsinclude three contacts; one for each phase of the 3-phase stator. In one embodiment, the 3-phase contactsare connected to each other, such that current may flow through any of the phases of the stator. In another embodiment, the voltage is provided to one of the 3-phase contactsof the statorand the brush is connected to the lead.

The insulation inspection systemmay be used to inspect a crown endof the statoras shown, a welded end, and/or other portion of the stator. The insulation inspection systemmay also be used to inspect individual electrical components and/or elements, an example of which is shown in. The crown endextends upward from a lamination stack. The welded end extends downward from the lamination stack. The bristlesmay be moved along different components of the statorto detect locations where insulative material is missing.

The insulation inspection systemincludes software and hardware with tunable A/D voltage thresholds utilized for flagging defects. As an example, the threshold for flagging a defect may be set to 5V but may be different for different applications. The control moduleimplements a detection algorithm that detects when the voltage across the terminals,drops below one of the A/D voltage thresholds and generates a visual and/or an audible signal to flag the defect detected.

The above-described voltage and current balancing circuit minimizes current levels at all points of operation independent of whether a short is present. The inclusion, selection, and arrangement of resistors and capacitor as described prevent large swings in voltage and current and thus prevent component degradation over time. This maintains current levels below thresholds associated with perceived and/or actual harm.